2Molecular Imaging & Diagnosis, Graduate School of Medical Sciences, Kyushu University, Japan
3Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Japan
4Department of Health science, Graduate School of Medical Sciences, Kyushu University, Japan
5Department of CT Clinical Science, Philips Healthcare, Cleveland, Ohio, USA
Methods: In twenty CAD patients, coronary CTA and invasive coronary angiography (CAG) were performed. CT-myocardial perfusion image (MPI) was reconstructed at 4 cardiac phases (0%, 40%, 60%, and 80% of the R-R interval), applying CT number measured in Hounsfield Unit (HU) as an estimate of perfusion. A myocardial segment with subendocardial low attenuation at endsystole was defined as subendocardial-systolic-hypoperfusion (SSH).
Results: Using >50% stenosis on CAG as standard, SSH diagnosed stenotic coronary territories with 63% sensitivity, 82% specificity, and 70% accuracy. Using >75% stenosis on CAG as standard, SSH diagnosed stenotic coronary territories with 73% sensitivity, 80% specificity, and 77% accuracy. The use of the SSH sign led to accurate diagnosis (result of CAG) in 9 of 60 territories (15%), which could not be assessed due to severe coronary calcification.
Conclusion: SSH is frequently seen in the stenotic coronary territories. SSH might provide powerful information when the assessment of coronary artery is made difficult by severe calcification.
Keywords: Coronary CT; Myocardial perfusion; Myocardial ischemia, Invasive coronary angiography
For all patients, an iodinated contrast agent (Iopamidol, 370 mgI/ml Iopamiron; Bayer Healthcare, Osaka, Japan) with a patient weight-based volume (0.7 ml × patient weight (kg)) was administered. The contrast agent was injected for 10 s followed by a 40 ml saline flush. Contrast agent and saline were injected at a rate of 4-5 ml/s into the antecubital vein via a 20-gauge catheter using a dual-head injector. Automatic bolus tracking was performed with a region of interest (ROI) placed in the aortic root. All CCTA scans were initiated 5 s after mean ROI contrast reached a pre-set threshold of 200 Hounsfield units (HU).
All patients underwent retrospectively ECG gated helical scans with ECG tube current modulation. The detector collimation was 2 × 128 × 0.625 mm, with a dynamic z-focal spot (ZFS), resulting in a sample collimation of 256 simultaneous slices of 0.625 mm thickness. The tube voltage was 100 or 120 kVp and the gantry rotation time was 0.27 s. An effective tube currentrotation time product (normalized to the pitch factor) ranging between 800 and 1050 mAs (depending on patient habitus) was used for the acquisition. Images were reconstructed with an individually adapted field of view (FOV) encompassing the heart, a matrix size of 512 × 512 pixels, an enhanced semi-smooth reconstruction kernel (CB), and a section thickness of 0.67 mm with an increment of 0.34 mm. The standard temporal resolution of 135 msec was further optimized via advanced adaptive multicycle reconstructions combining data from consecutive cardiac cycles[4]. A dedicated cardiac gating algorithm (Beat-to-Beat Variable Delay Algorithms, Philips Healthcare, Cleveland OH, USA)[5] was used, that enabled the detection and reconstruction of the same physiological cardiac phase of interest. In addition,
Number of patients |
|
20 |
Age (years) |
|
66.0 ± 12.2 (range 28 - 81) |
Body mass index (kg/m2) |
|
25.3 ± 4.1 (range 20.8 - 33.2) |
Male gender |
|
14 (70%) |
Hypertension |
|
13 (65%) |
Dyslipidemia |
|
7 (35%) |
Diabetes |
|
13 (65%) |
Family history of CAD |
|
4 (20%) |
Cigarette smoking |
|
11 (55%) |
End-stage renal disease |
|
3 (15%) |
Peripheral vascular disease |
|
2 (10%) |
Diagnostic capability of SSH to detect CAD, based on both > 50% and > 75% luminal stenotic territory on CAG, was calculated. SSH was considered to be correct if SSH were seen in the same myocardial segments with coronary stenosis on CAG. We calculated sensitivity, specificity, positive predictive value, and negative predictive value for SSH.
In our study, the discrepancy of coronary stenosis between CCTA versus CAG was observed in 12 coronary territories; 2 territories of over diagnosis, 1 territory of under diagnosis, 9 territories of not assessed due to severe calcified plaques. The use of the SSH sign led to accurate diagnosis (result of CAG) in 10 of these 12 territories. Representative cases were indicated in Figures 2 and 3. Nine territories of 60 territories (15%) could not be assess with CCTA, whereas all territories could be assessed with both CCTA and SSH.
Total |
CCTA |
CAG |
|
SSH(+) |
>50% |
>75% |
|
Patient |
19/20 (95%) |
20/20 (100%) |
18/20 (90%) |
Vessel territory |
28/60 (47%) |
38/60 (63%) |
30/60 (50%) |
Distribution |
SSH(+) |
>50% |
>75% |
RCA |
8/20 (40%) |
10/20 (50%) |
9/20 (45%) |
LAD |
16/20 (80%) |
18/20 (90%) |
17/20 (85%) |
LCX |
4/20 (20%) |
10/20 (50%) |
4/20 (20%) |
The threshold value of a coronary stenosis (CAG) |
||
50% |
75% |
|
Sensitivity |
63.2% (24/38) |
73.3% (22/30) |
Specificity |
81.8% (18/22) |
80% (24/30) |
PPV |
85.7% (24/28) |
78.6% (22/28) |
NPV |
56.3% (18/32) |
75% (24/32) |
Accuracy |
70% (42/60) |
76.7% (46/60) |
The use of the SSH sign led to accurate diagnosis (result of CAG) in 10 of the 12 territories deviated coronary stenosis between CCTA versus CAG. The presence of SSH might provide useful additional information when the assessment of coronary artery is made difficult by severe calcification.
The decline of myocardial contrast enhancement is due to reduction of myocardial blood flow in the coronary artery supplying blood to the ischemic region of the myocardium. The endocardium is the area of the left ventricle most vulnerable to the effects of hypoperfusion and ischemia. As the result, the ischemic area exhibits subendocardial low attenuation (myocardial enhancement) compared to the normal regions [1].
Although several previous studies have demonstrated possibility of rest CTP imaging to identify myocardial ischemia Spiro AJ et al [3, 8]. stated that resting cardiac 64-MDCT dose not reliably detect myocardial ischemia identified by radionuclide imaging [9]. The mean body mass index for their patients was 30, supposing that the majority of patients were obese. This affects increase in signal noise and decrease in myocardial enhancement, resulting miss - diagnosis by rest CTP imaging. On
the other hand, the mean body weight for our Japanese patients was about 60kg, and the mean body mass index was about 20. Patient size is suitable for getting high contrast and artifact less image. In addition, the scan time of 256-slice MSCT is less than 5 seconds and that of 64-slice, and the timing is the early phase of myocardial enhancement during the first pass. The short scan time of 256-slice MSCT can amplify the difference in myocardial enhancement between systole and diastole. Further, 256-slice CT with high temporal resolution can achieve motion artifact less in myocardial imaging at systole as well as diastole.
With a standard temporal resolution of 135 ms further optimized via cardiac adaptive multi-cycle reconstructions, the end-systolic rest phase can be successfully targeted using the 256-slice MSCT enabling the user to accurately trace myocardial boundary. With a wide coverage of 8 cm, the contrast bands are minimized, thus also reducing their impact on attenuation changes [10, 11]. The resulting short scan times of 256-slice MSCT (<5 s for a typical cardiac anatomy) could facilitate optimization of the contrast volume needed to help enable cardiac imaging at the peak coronary enhancement [12].
Limitations: This was single-center pilot study with a small number of patients. The CCTA scans were triggered based on a pre-determined threshold of the mean HU of the contrast arrival in the aortic root – while this is targeting the early phase of the myocardial enhancement during the first pass, the timing may not be optimized for the peak enhancement of the myocardium. In addition, our investigations did not quantify the measures commonly associated with perfusion (blood flow, volume, etc). These are typically extracted from dynamic perfusion scans. However, since these scans could result in an increased radiation exposure, we limited our investigations to a single CCTA scan in the interest of keeping the radiation exposure low.
In conclusion, SSH was quantified by subendocardial and subepicardial attenuation using retrospective resting ECGgate CCTA. SSH was present in a high rate in stenotic coronary territories confirmed by CAG, and could provide additional hemodynamic information with the detection of CAD (especially =>75% stenosis) with high diagnostic accuracy.
- Higuchi K, Nagao M, Matsuo Y, et al. Evaluation of chronic ischemic heart disease with myocardial perfusion and regional contraction analysis by contrast-enhanced 256-MSCT. Japanese journal of radiology. 2013; 31(2): 123-132.
- Nagao M, Matsuoka H, Kawakami H, et al. Myocardial ischemia in acute coronary syndrome: assessment using 64-MDCT. AJR American journal of roentgenology. 2009; 193(4): 1097-1106.
- Nagao M, Matsuoka H, Kawakami H, et al. Quantification of myocardial perfusion by contrast-enhanced 64-MDCT: characterization of ischemic myocardium. AJR American journal of roentgenology. 2008; 191(1): 19-25.
- Manzke R, Grass M, Nielsen T, Shechter G, Hawkes D. Adaptive temporal resolution optimization in helical cardiac cone beam CT reconstruction. Medical physics. 2003; 30(12): 3072-3080.
- Vembar M, Garcia MJ, Heuscher DJ, et al. A dynamic approach to identifying desired physiological phases for cardiac imaging using multislice spiral CT. Medical physics. 2003; 30(7): 1683-1693.
- Walker MJ, Olszewski ME, Desai MY, Halliburton SS, Flamm SD. New radiation dose saving technologies for 256-slice cardiac computed tomography angiography. Int J Cardiovas Imag. 2009; 25: 189-199.
- Cerqueira MD, Weissman NJ, Dilsizian V et al. Standardized myocardial segmentation and nomenclature for tomographic imaging of the heart:A statement for healthcare professionals from the Cardiac Imaging Committee of the Council on Clinical Cardiology of the American Heart Association. Circulation. 2002; 105(4): 539-542.
- Busch JL, Alessio AM, Caldwell JH et al. Myocardial hypo-enhancement on resting computed tomography angiography images accurately identifies myocardial hypoperfusion. Journal of cardiovascular computed tomography. 2011; 5(6): 412-420.
- Spiro AJ, Haramati LB, Jain VR, Godelman A, Travin MI, Levsky JM. Resting Cardiac 64-MDCT Does Not Reliably Detect Myocardial Ischemia Identified by Radionuclide Imaging. Am J Roentgenol. 2013; 200(2): 337-342.
- Herzog C, Arning-Erb M, Zangos S, et al. Multi-detector row CT coronary angiography: influence of reconstruction technique and heart rate on image quality. Radiology. 2006; 238(1): 75-86.
- Klass O, Walker M, Siebach A, et al. Prospectively gated axial CT coronary angiography: comparison of image quality and effective radiation dose between 64-and 256-slice CT. European radiology. 2010; 20(5): 1124-1131.
- Bae KT. Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches. Radiology. 2010; 256(1): 32-61.